The invention relates to mobile telephone stations and more particularly for a method and apparatus for dual tone multiple frequency (DTMF) signaling between mobile stations in a tandem free operation (TFO) mode without switching to a tandem operation mode.
The known operation of mobile-to-mobile communication arrangement 100 is shown in FIG. 1 and is referred to as tandem operation. In tandem operation, if mobile station A (MS A) 102 attempts to send a DTMF signal to mobile station B (MS B) 124, then MS A 102 encodes a message with the DTMF signal according to the IS-95 standards and sends the message over the air. The encoded DTMF signal is received by coder/decoder (CODEC) A 108, decoded by CODEC A 108, and sent over a high bit rate line 112 to CODEC B 118. CODEC B encodes the DTMF signal and sends it to MS B 124. MS B 124 decodes the encoded DTMF signal and uses it. CODEC A 108 and CODEC B 118 know the format of their respective mobile stations and will provide any protocol or format conversion that is necessary, such as CDMA to TDMA. If both MS A 102 and MS B 124 use CDMA, i.e. are both digital, then CODEC A 108 and CODEC B 118 are not adding anything by their operation except some quantization noise, distortion and some time delay. The distortion and the delay are reasons that bypass or tandem free operation (TFO) mode standards are open for suggestions in area.
The presently proposed TFO standards do not include a way to provide mobile-to-mobile DTMF signaling without first switching into tandem operating mode and go through CODECs. The IS-95 standards for CDMA provide for Reverse (Uplink) DTMF Signaling Messages and Forward (Downlink) DTMF Signaling Messages; however, there is presently no end to end DTMF signaling mechanism in the proposed TFO mode. Because the TFO standards are presently without a DTMF signaling mechanism in TFO mode, it is presently necessary to go into tandem operation mode (i.e., without TFO) and use CODECs whenever DTMF signaling is needed.
According to the presently proposed TFO standards, going out of TFO mode could require about 60 msec. According to the BellCore standards for DTMF detection, a DTMF energy burst of a duration of 40 msec or more should be detected successfully by the station to which it is directed. Thus, it can be seen that a waiting period of 60 msec could very well cause a DTMF character and/or digit not to be detected at the receiving mobile station.
Further, wireless local loop (WLL) applications are becoming a very vital part of the wireless applications and products. Often in WLL, a Network Interface Unit (NIU) is used as the mobile. End-users can hook up ordinary, off-the-shelf landline equipment (e.g., answering machines, POTS phone sets, etc.) to their NIUs. Therefore it is important to ensure the reliable transmission of DTMF tones from one mobile (e.g. MS A 102) to another mobile (e.g. MS B 124), especially when MS B 124 is a NIU, and to be able to reliably use any of the NIU peripherals (e.g., answering machines) through the use of signaling by way of DTMF tones.
Thus, there is a need in the art for TFO with reliable DTMF signaling.
There is also a need in the art for mobile to mobile operation without needless distortion and delay caused by unnecessary coding and decoding by CODECs.
This proposal makes it possible to support mobile station-to-mobile station DTMF signaling in TFO mode, without having to switch into tandem operation mode when the mobile stations use compatible wireless digital communication techniques.
In accordance with one aspect of the invention, the aforementioned problems are addressed and an advance in the art achieved by providing a method for sending a DTMF tone burst from a first MS to a second MS while a call is in progress. This method includes the steps of: establishing a TFO mode for this call; directing the first MS to transmit a DTMF tone burst representing at least one DTMF character; sending an IS-95 reverse burst DTMF signaling message from the first MS to a first TFO processor; extracting DTMF information from the burst DTMF signaling message received by the first TFO processor and forming a TFO frame containing this DTMF information; and transmitting this TFO frame to a second TFO processor. Upon receiving the DTMF information in the TFO frame, the method continues with the steps of: sending a DTMF signaling acknowledgment message from the second TFO PROC to the first TFO PROC in another TFO frame; extracting the DTMF information from the TFO frame received by the second TFO PROC and triggering the generation of an IS-95 forward burst DTMF signaling message; transmitting this forward burst DTMF signaling message to the second MS; and generating DTMF tones based on the DTMF information of the DTMF signaling message received by the second MS.
In accordance with another aspect of the invention, the aforementioned problems are addressed and an advance in the art achieved by providing a method for sending a continuous DTMF tone from a first MS to a second MS while a call is in progress. This method includes the steps of: establishing TFO mode for this call; directing the first MS to transmit a continuous DTMF tone representing at least one DTMF character; sending an IS-95 reverse burst DTMF signaling message from the first MS to a first TFO processor; extracting DTMF information from the continuous DTMF signaling message received by the first TFO PROC and forming a TFO frame containing this DTMF information; and transmitting this TFO frame to a second TFO PROC. Upon receiving the DTMF information in the TFO frame, the method continues with the steps of: sending a DTMF signaling acknowledgment message from the second TFO PROC to the first TFO PROC in another TFO frame; extracting the DTMF information from the TFO frame received by the second TFO PROC and triggering the generation of an IS-95 forward burst DTMF signaling message; transmitting this forward burst DTMF signaling message to the second MS; and generating DTMF tones based on the DTMF information of the DTMF signaling message received by the second MS.
In accordance with another aspect of the invention, the aforementioned shortcomings of the art are addressed and an advance in the art provided by an apparatus for sending a burst of DTMF tones from one mobile station to another mobile station while a call is in progress. The apparatus includes: TFO processors for establishing TFO mode for this call; a manual input device for directing a first mobile station to transmit a burst DTMF digit or multiple DTMF digits; an IS-95 reverse burst DTMF signaling message unit for sending an IS-95 reverse burst DTMF signaling message from the first mobile station to a first TFO processor; the first TFO processor extracting DTMF information from the DTMF signaling message received by the first TFO processor and forming a TFO frame containing this DTMF information; the TFO processor having an output for transmitting this TFO frame to a second TFO processor; the second TFO processor having means for sending a DTMF signaling acknowledgment message to the first TFO processor in another TFO frame; the second TFO processor also extracts the DTMF information from the TFO frame received from the first TFO processor and triggering the generation of an IS-95 forward burst DTMF signaling message; the second TFO processor having an output for transmitting the burst DTMF signaling message to the second mobile station; and means for generating DTMF tones based on the DTMF signaling message received by the second mobile station.